Invalid IR test errors

module.verify() will report errors if our generetad IR is not valid
this verification can either be activated by "cargo test --features=verify" or in cargo.toml

failing tests

• codegen::tests::debug_tests::expression_debugging::external_impl_added_as_external_subroutine

• #696

• #697

• #736

• #698

• codegen::tests::string_tests::function_returning_generic_string_should_return_by_ref

• codegen::tests::string_tests::using_a_constant_var_string_should_be_memcpyable

• codegen::tests::typesystem_test::small_int_varargs_get_promoted_while_32bit_and_higher_keep_their_type

• correctness::datatypes::function_return_string_by_ref_via_inout

• correctness::external_functions::string_sized_pointer_variadic_call

• correctness::external_functions::sized_pointer_variadic_call

• correctness::functions::by_ref_and_by_val_mixed_function_call

• correctness::strings::string_as_function_parameters

• correctness::strings::string_as_function_parameters_cast

• correctness::strings::string_as_function_parameters_internal

• correctness::strings::wstring_as_function_parameters

• correctness::strings::wstring_as_function_parameters_cast

• correctness::strings::assigning_global_strings_in_program_by_passing_sized_strigs

• correctness::functions::mux_string_literal

Start by running the verification described in the issue with cargo test --features=verify, then inspect the unchecked codegen and correctness tests listed there. Trace the reported invalid IR back through the relevant test and generated output. Done means the affected tests no longer report invalid IR under verification.